The present invention relates to a powered exhaust fan and in particular to an internally mounted powered exhaust fan for building structures.
Originally, before the introduction of insulation, ventilation occurred by air flowing freely through the ceilings of building structures into attic airspaces. During warmer seasons, it was advantageous to allow this air to passively ventilate through roof vents, to cool the structure. During cooler seasons the passive vents were closed off to trap the heat within the home.
A well known form of passive ventilation is a system of ridge and soffit vents. Ridge vents include a slot along a ridge or roof peak, typically where the warmest air collects. This slot is covered with another peaked structure which blocks out the elements and reduces airflow into the structure through the ridge vent. Soffit vents appear on the underside of the overhanging portion of the roof structure. Air flow occurs when the positive pressure of the ridge vent pulls air upwards through the soffit vents.
Passive ventilation was sufficient for most structures until recent advances in building technology and insulation methods led to the construction of more airtight buildings. In a newer building heavy insulation is typically used in the ceiling obviating the need for warm air in the attic to keep the structure warm. In fact, trapped warm air has become a liability. With the concurrent addition of more water sources in newer structures, such as bathrooms, shower, humidifiers etc., the trapped air has a tendency to become very humid. This increased humidity causes dampness in the structural elements of the building resulting in damage to the structural elements after successive freeze-thaw cycles.
Another advance concurrent to improved building insulation has been the advent of common air conditioning. Air conditioning cools outside, or ambient air, for building structure use. Even with the cooling effect of passive ventilation the ventilated air is still warmer than the mechanically cooled air within the building. This creates a "hot-plate" effect where the warm ceiling of the structure radiates heat into the structure, partially undoing the cooling effect of the air conditioner.
These problems have led to a need for improvements over traditional passive ventilation. The prior art has attempted to address these problems through the addition of powered fans to the ventilation systems. U.S. Pat. No. 3,085,490 to Field discloses a box structure containing a powered fan and a vent. The box structure physically sits on top of the roof over a rectangular hole cut into the rooftop. The powered fan draws air through the hole in the roof top and forces this air through the vent in the box structure. This invention is an improvement over a passive vent of the same size but still has several drawbacks. One drawback is that the Field ventilation system is aesthetically unacceptable for many applications. The box structure of the field ventilation system sits on top of the roof and is not similar to the roof in shape or in the material used for its construction. Another drawback is that the Field ventilation system creates a stronger flow of air with its powered fan but only in a narrow stream, leaving significant unmoving or "dead" air within the attic. Any potential remedy would be at an increased expense and would have a greater adverse impact on the appearance of the structure.